My first statement would be just install sparky mate.If you want to modify what you have you will have to find the files they use and add them to your install.It's pretty complicated to get all the icons and backgrounds and fonts and whatever else they are using.Go do some google searching on how to modify themes in MATE.

It might be a custom theme that Sparky tweaks, and so would be in some Sparky package, not on Debian repos. If you install and run neofetch on Sparky, it should be able to tell you what theme you're using.

njohn wrote:Have Debian 9 Buster with Mate Desktop. I want to change the theme to the one used in Sparky Mate.How do I do that?

if i were you, i'd tackle it like this:- find out if the software components (window manager, ui toolkit) are the same or compatible on your system as on sparky's (i suspect the window manager could be different, but the gtk themes are compatible)- a web search along the lines of "linux install theme how to"- another web search "linux download themes" or maybe even "linux sparky theme"i'm pretty sure you will end up at gnome-look.org at some point, where you could use "sparky" for a search, or maybe even find something awesomer.